Metal-core PC board for insertion into the housing of an electronic device

ABSTRACT

A PC board to be populated with electronic components, for insertion into the housing of an electronic device, has a core made of two metal plates connected together and spaced apart by reinforcing ribs, said plates being provided with a copper-invar layer and with a cover layer formed by several layers of polyimide film. To achieve high rigidity and good heat transfer, the metal plates are made of aluminum or an aluminum alloy and are fastened in the housings by means of gibs and cotters.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a metal-core PC board for insertion into thehousing of an electronic device. The core consists of two metal platesjoined together and spaced apart by metal ribs, on the outer surfaces ofwhich core multilayer insulating layers are provided. The marginal areasof at least two opposite lateral edges of the metal-core PC board arenot coated.

The requirements for such metal-core PC boards, which are usuallypopulated with electronic components, specify in particular, that theheat generated during operation of the electronic components can beconducted away well, that high dimensional stability of the board isthus guaranteed so as not to endanger the printed conductors, and thatlow weight is also achieved to make the electronic devices equipped withthe boards correspondingly light.

A metal-core PC board for insertion into a housing of an electronicdevice, with the core consisting of two metal plates spaced apart fromone another and connected together by metal ribs, with multilayerinsulating layers being provided on the outer surfaces of the core, andwith the marginal areas of at least two opposite lateral edges of themetal-core PC board not being coated (sliding margins) is known fromEuropean Patent document EP-0 124 128 A1.

A metal-core PC board is also known from German Patent document DE-88 11949 U1 whose edges can be clamped by a spreading device to secure themin a housing. In this known board, heat is advantageously conducted awayfrom the metal-core PC board into the housing.

It has been shown that individual measures like those known from theEuropean publication EP-0 124 128 A1 which constitutes the species orfrom the German publication DE-88 11 949 U1 are insufficient to meet therequirements imposed on metal-core PC boards regarding high dimensionalstability, low weight, and good heat dissipation.

Hence the goal of the present invention is to provide a metal-core PCboard of the above-mentioned type which exhibits high dimensionalstability when exposed to temperature differentials, allows optimal heatdissipation through the housing, and is also low in weight.

This goal is achieved according to the present invention by a metal-corePC board for insertion into a housing of an electronic device, with thecore consisting of two metal plates spaced apart from one another andconnected together by metal ribs, with multilayer insulating layersbeing provided on the outer surfaces of the core, and with the marginalareas of at least two opposite lateral edges of the metal-core PC boardnot being coated (sliding margins). The core consists of aluminum or analuminum alloy. Copper-invar (nickel steel) layers are applied to theouter surfaces of the core. A polyimide insulating layer composed ofseveral layers is applied to the copper-invar layers. The marginalareas, i.e., the sliding margin (g), is free of ribs and thecorresponding metal plates can be spread apart in the vicinity of thesliding margin (g) through the use of gibs and cotters.

By making the metal core of aluminum or an aluminum alloy, especiallygood heat conduction and hence heat dissipation is achieved. Thestiffening ribs serve for heat compensation. By placing the plasticcover layer on top of the copper-invar layer, improved heat conductioninto the metal core and from the latter to the housing is achieved.

The thickness, spacing, and number of the metal plates or plastic filmsare preferably chosen as will be described herein.

Securing the metal-core PC board in the housing through the use of a giband cotter in an area of the sliding margin that is kept free of anyreinforcing ribs contributes to the heat transfer between the metal-corePC board and the housing due to the increased bilateral fit of the metalplates against the grooved wall of the housing.

In a preferred embodiment of the invention, the gib and cotter isfastened to one of the metal plates. By fastening the gib and cotter toone of the metal plates, the need for manual adjustment is eliminatedwhen clamping it in place, and such fastening provides protectionagainst loss.

One embodiment of the metal-core PC board according to the inventionwill now be described with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a metal-core PC board according to theinvention;

FIG. 2 is a partial section view through the PC board along Line II--IIin FIG. 1; and

FIG. 3 is a partial section view through the PC board along LineIII--III in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1, the metal-core PC board, shown in a top view, is designatedgenerally by 1. The board 1 shown is rectangular in shape; however, adifferent contour is also possible. However, two parallel straightlateral edges must always be provided opposite one another to permit thesliding of the board into a suitable housing with parallel guides. Thelarge edge length of the board is designated L. A cover layer 33 on theboard, made of polyimide film, is made shorter than the length L of thelong edge, so that the two opposite short lateral edges each have asliding margin g which is kept free of coating. The board 1, made in theform of a double-rib board, is provided with reinforcing ribs 13, 14running lengthwise and crosswise to increase the rigidity, withreinforcing ribs 14 running along length L. A marginal area b of theboard is kept free of the reinforcing ribs 14 along the lateral edgesprovided with the sliding margin g. Marginal edge b extends over anapproximate length of 0.1 to 0.2 L. In the intermediate space of thedouble rib plate bridged by the reinforcing ribs 13, 14, gibs andcotters 2 are located in the vicinity of sliding margins g and serve tospread the individual boards of the double-rib board apart.

The structure of the metal-core PC board is clear from the partial crosssection shown in FIG. 2. The core consists of two spaced metal plates11, 12 connected together by reinforcing ribs 13, 14. On the outersurfaces of metal plates 11, 12, a copper-invar layer 32 is applied, onwhich a plastic cover layer 33 rests. The copper-invar layer is glued tothe metal plates by an adhesive and the plastic cover layer is glued byan adhesive to the copper-invar layer. The plastic cover layer consistsof a multilayer polyimide film, with a maximum of four film layerspreferably being used. The sliding margin g of metal plates 11, 12 whichis kept free of the coating, is indicated along the short lateral edgesof the metal-core PC board. By means of this sliding margin 9, themetal-core PC board can be slid into suitably designed guide grooves ina housing. In FIG. 2 this housing is indicated by a dot-dashed line andgiven the reference numeral 5. The board can be secured in the guidegrooves by virtue of the fact that the two metal plates 11, 12 can bespread apart in marginal area b, in each case with the help of a gib andcotter 2.

The gibs and cotters used consist of a plurality of wedges 22 resting ona screw bolt 21 and tensionable in the axial direction by means of thescrew bolt 21, in the course of which action they spread themselvesoutward in accordance with the arrows shown in FIG. 2 (bottom) and arepressed against the inner surfaces of metal plates 11, 12. The gibs andcotters 2 can be provided as loose parts which must then be moved andtightened in the correct position and can be fastened unilaterally toone of metal plates 11, 12.

The drawings shown considerably enlarged in FIGS. 2 and 3 are not toscale. The dimensions and layer thicknesses must be chosen in accordancewith the following information. In one example of a metal-core PC boardthat is shown, the following advantageous dimensions have been selected:L=250 mm, a=5 mm, b=25 mm, g=12 mm, dd=5 mm, thickness of copper-invarlayer=0.2 mm, thickness of plastic layer made of polyimide film=0.3 mm,with four film layers.

In addition to gluing, the cover layer made of a copper-invar layer andpolyimide films can be secured by screws or rivets to metal plates 11,12.

Advantageously, metal plates 11, 12 have a thickness d in a range from1×10³ to 5×10³ L, where L is the long edge length of the board 1.Further, the spacing (a) of the metal plates 11, 12 is in the range from1×10² to 5×10² L. Also, the copper-invar layer 32 is a sheet having athickness in the range of from 4×10⁴ to 12×10⁴ L.

As shown in FIG. 2, the copper-invar layers 32 are glued using a siliconrubber adhesive 31 to the metal plates 11, 12. The cover layer 33 has amaximum of 4 film layers. Also, the thickness of the cover layer 33 isin the range from 1×10³ to 2×10³ L.

In preferred embodiments, along the lateral edges of the board 1 havingthe sliding margins g, the marginal area b equals 0.1 L to 0.2 L and iskept free of the reinforcing ribs.

In a further preferred embodiment, the gib and cotter 2 are fastened toone of the metal plates 11, 12.

We claim:
 1. A metal-core PC board insertable into a housing of anelectronic device, the metal-core PC board comprising:a core comprisingtwo metal plates spaced apart from one another and metal ribs connectingthe two metal plates together, said core being formed of one of analuminum and aluminum alloy; copper-invar layers applied to the outersurfaces of said core; a polyimide insulating layer composed of severallayers applied to the copper-invar layers; wherein said copper-invarlayers and said polyimide insulating layer are arranged on the outersurface of said core such that sliding marginal areas of at least twoopposite lateral edges of the metal-core PC board are not coated; gibsand cotters arranged between the two metal plates in a vicinity of thesliding marginal areas such that the two metal plates are spread apart;and wherein the sliding marginal areas are free from any of said metalribs.
 2. The metal-core PC board according to claim 1, wherein each ofthe two metal plates have a thickness d in a range from 1×10³ to 5×10³L, where L is a long edge length of the metal-core PC board.
 3. Themetal-core PC board according to claim 1, wherein a spacing between thetwo metal plates is in a range of from 1×10² to 5×10² L, where L is along edge length of the metal-core PC board.
 4. The metal-core PC boardaccording to claim 1, wherein a spacing between the two metal plates isin a range of from 1×10² to 5×10² L.
 5. The metal-core PC boardaccording to claim 4, wherein each of the copper-invar layers is a sheetwith a thickness in a range of from 4×10⁴ to 12×10⁴ L.
 6. The metal-corePC board according to claim 1, wherein each of the copper-invar layersis a sheet with a thickness in a range of from 4×10⁴ to 12×10⁴ L, whereL is a long edge length of the metal-core PC board.
 7. The metal-core PCboard according to claim 1, wherein the copper-invar layers are gluedusing a silicone rubber adhesive to the metal plates.
 8. The metal-corePC board according to claim 1, wherein the polyimide insulating layerhas a maximum of four film layers.
 9. The metal-core PC board accordingto claim 1, wherein a thickness of the polyimide insulating layer is ina range of from 1×10³ to 2×10³ L, where L is a long edge length of themetal-core PC board.
 10. The metal-core PC board according to claim 1,wherein the metal-core PC board, along the lateral edges with thesliding marginal areas, has a marginal area =0.1 L to 0.2 L, which iskept free of the metal ribs, where L is a long edge length of themetal-core PC board.
 11. The metal-core PC board according to claim 1,wherein the gibs and cotters are fastened to one of the two metalplates.